JPH03203754A - Electrostatic charging device - Google Patents

Abstract

PURPOSE:To restrain an ozone generating quantity and to prevent unevenness in electro static charging on a surface to be electrostatically charged by disposing a resistance functioning as a discharge electrode and having a part opposite to a body to be electrostatically charged where a voltage is impressed on an electrostatic charging blade. CONSTITUTION:A photosensitive body 1 rotates clockwise and passes through the leading edge part of a blade substrate 11 which abuts on the surface of the photosensi tive body 1. At this time, the voltage which is obtained by superposing an AC on a DC by a current 13 is impressed between a lead electrode 14 and the conductive base substance 2 of the photosensitive body 1 functioning as the counter-electrode of the lead electrode 14. Since the voltage is impressed on the resistance 15 which is disposed on the electrostatic charging blade part while functioning as the discharge electrode in such a way, corona discharging occurs between the resistance 15 and the photosensitive body 1, and the surface of the photosensitive body 1 is uniformly electrostatically charged to a prescribed polarity. Thus, there is no possibility of the occurrence of the unevenness in electrostatic charging in a stripe state on the surface of the photosensitive body, so that the ozone generating quantity and the deterioration of the photosensitive body can be restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a charging device that charges the surface of an object to be charged to a predetermined polarity.

[Conventional technology]

For example, a photoreceptor used in an image forming apparatus such as an electronic copying machine, a printer, or a facsimile is charged to a predetermined polarity prior to exposure in order to form an electrostatic latent image on its surface.

In order to charge such an object to be charged, a corona discharger that generates corona discharge by applying a voltage to a charge wire has been widely used. However, when a corona discharger is used, it is necessary to apply a high voltage to the charge wire, so there is a problem that a large amount of ozone is generated during discharge.

Therefore, a semi-conductive resistor blade is brought into contact with the surface of the photoreceptor, and a DC voltage is applied to this blade. Charge is injected into the photoreceptor by leakage current to the photoreceptor, and this is charged. A device has been proposed. However, according to this charging device, since the charging operation is performed while the blade is in direct contact with the surface of the photoreceptor and the two are moved relative to each other, sled-like charging unevenness occurs on the surface of the photoreceptor. If such unevenness occurs, smudges will also be formed on the image after development, leading to deterioration in image quality.

A charging device has also been proposed in which a charging roller made of a resistor layered around a conductor is brought into contact with a photoconductor, and the photoconductor is charged by the voltage applied to the conductor. Since it is necessary to rotate the roller,
The structure of the device becomes complicated and the cost increases.

Furthermore, a charging device that charges the surface of the photoreceptor by applying a DC voltage to a charging member made of a conductor whose surface is coated with a resistor and which is disposed close to the surface of the photoreceptor, thereby causing no discharge. has also been proposed (Japanese Unexamined Patent Publication No. 58-76851)
(see publication). According to this configuration, the charging member is separated from the photoreceptor, and there is no need to rotate and open the charging member, so that the drawbacks seen in the two prior art examples described above do not occur.

However, the surface of the photoreceptor has slight undulations and depressions, and the circumferential surface is often eccentric. When such a photoreceptor is used, the distance between the moving photoreceptor surface and the charging member constantly changes. The size of this interval has a great effect on the discharge, and as the interval changes, the amount of charge on the surface of the photoreceptor becomes non-uniform, which may reduce the quality of the image.

[Problem to be solved by the invention]

An object of the present invention is to provide a charging device that eliminates the above-mentioned conventional drawbacks with a simple configuration.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention is arranged such that the tip part is in contact with the charged object opposite to the moving direction of the charged object and a wedge-shaped gap is formed between the charged object and the charged object. The present invention proposes a charging device including a charging blade having a resistor as a discharge electrode to which a voltage is applied at a portion of the blade facing the object to be charged.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an example of an electronic copying machine using a charging device according to the present invention, and first, its overall configuration will be briefly explained.

A drum-shaped photoreceptor 1 has a cylindrical conductive substrate 2 and a photosensitive layer 3 laminated on its surface, and is rotated clockwise in the figure. At this time, the surface of the photoreceptor is uniformly charged to a predetermined polarity by a charging device 4, which will be described in detail later, and the charged surface of the photoreceptor is image-exposed in an exposure section 5. In this way, an electrostatic latent image is formed on the surface of the photoreceptor, and this latent image is converted into a toner image by the developing device 6.

This toner image is transferred to a transfer paper 7, and the toner remaining on the surface of the photoreceptor after the transfer is cleaned by a cleaning device 20, and then the surface of the photoreceptor is subjected to a charge-eliminating action by a charge-eliminating device comprising a charge-eliminating lamp 8.

The charging device 4 has a charging blade 9, as shown in an enlarged view in FIG. A wedge-shaped gap 10 is formed between the charging blade 9 and the photoreceptor 1 so as to be in contact with the surface of the photoreceptor 1. That is, the charging blade 9 is positioned in a so-called counter direction with respect to the photoreceptor 1, and its tip portion is in contact with the surface of the photoreceptor 1.

The charging blade 9 illustrated in FIGS. 1 and 2 has a blade base plate 11 made of an elastic plate, the proximal end of which is fixed to the machine frame of the copying machine main body via a holder 12, and the tip end of the blade base plate 11. The blade substrate is in pressure contact with the surface of the photoreceptor 1 due to its own elasticity.

A charging blade portion facing the surface of the photoreceptor 1 with a wedge-shaped gap 10 is provided with a lead electrode 14 made of a layered conductor connected to a power source 13, and a resistor as a discharge electrode covering the entire lead electrode 14. The resistor 15 is integrally provided, and in the example shown in FIG. 2, the resistor 15 is not in contact with the photoreceptor 1.

As described above, the photoreceptor 1 rotates clockwise in FIG. 1 and passes through the tip of the blade substrate 11 that comes into contact with the surface of the photoreceptor 1. At this time, a voltage in which a direct current and an alternating current are superimposed is applied by the power source 13 between the lead electrode 14 and the conductive base 2 of the photoreceptor 1, which is its counterpart electrode. Since voltage is applied to the resistor 15 in this way, corona discharge occurs between the resistor 15 and the photoreceptor 1, and the surface of the photoreceptor 1 is uniformly charged to a predetermined polarity (negative polarity in this example). be done.

The fact that the surface of the photoreceptor is charged by corona discharge was confirmed by an experiment in the dark when a light emission (discharge) phenomenon occurred in the gap 10.
It is clear from the fact that

In this way, the charging device 4 shown in FIGS. 1 and 2 does not inject charge with a resistor blade that comes into contact with the photoreceptor 1, but rather charges the surface of the photoreceptor by corona discharge. Therefore, there is no possibility that sushi-like charging unevenness will occur on the surface of the photoreceptor. The starting voltage for this discharge is usually on the order of several hundred volts, and the applied voltage can be significantly lowered compared to conventional corona dischargers that generate corona discharge by applying a voltage of several thousand volts to a charge wire. Therefore, the amount of ozone generated can be effectively suppressed and deterioration of the photoreceptor can be suppressed.

Further, unlike conventional charging devices using f-electrification rollers, there is no need to drive the charging blade, so the structure of the device can be simplified and costs can be reduced.

Furthermore, the surface of the photoreceptor 1 may have undulations and depressions,
Even if the photoconductor itself is eccentric, the blade substrate 11 in contact with the surface of the photoconductor 1 follows the photoconductor surface while elastically deforming according to the unevenness and eccentricity, so that the resistance between the resistor 15 and the photoconductor 1 is The size of the gap 10 between the surfaces will always be constant. This prevents the problem of uneven charging on the surface of the photoreceptor, which occurs in conventional charging devices in which the charging member is placed apart from the photoreceptor, making it possible to always obtain high-quality images (toner images). I can do it.

Furthermore, in the charging device 4 shown in FIGS. 1 and 2,
Since the tip of the charging blade 9 is in contact with the photoconductor 1 in a direction opposite to the direction of movement, this tip functions to clean the photoconductor 1 and remove toner and other substances from the gap 10 where corona discharge occurs. It is possible to prevent dust from entering and generate stable discharge.

If the position of the charging blade 9 is reversed from that shown in FIGS. 1 and 2 and is placed in the trailing direction with respect to the photoreceptor 1,
Dust enters the gaps between these, causing uneven corona discharge. As a result, not only does the charging potential on the surface of the photoreceptor become uneven, but also dust passes between the charging blade and the photoreceptor, which causes the blade to move away from the photoreceptor, causing the discharge gap to fluctuate. Even in this case, there is a risk that uneven charging will occur.

Furthermore, since the charging blade itself has a cleaning function for the photoreceptor 1 as described above, the cleaning device 20 shown in FIG. It can also be configured to perform cleaning using only the blade.

The tip of the charging blade 9, in this example, the blade substrate 1
The tip of the photoreceptor 1 is in contact with the surface of the photoreceptor 1, but the surface of the photoreceptor 1 is not charged by friction due to this contact, or even if it is charged, it is frictionally charged due to the charged polarity (negative polarity) due to corona discharge of the resistor 15. Blade substrate 1 to be charged
It is desirable to choose the material of 1. If the surface of the photoreceptor is significantly tribo-charged to the positive polarity side by the charging blade 9, uneven charging will occur on the surface of the photoreceptor after it has been negatively charged by corona discharge, which may cause density unevenness in the image. It is from. However, even if the amount of charge due to frictional charging is positive, it is small, or if it is triboelectrically charged to the same polarity as the charging polarity due to corona discharge, the resistor 1
This frictional electrification can be corrected by the corona discharge caused by the photoreceptor 5, and the surface of the photoreceptor after passing through the charging device 4 can be uniformly charged to a predetermined negative polarity. As described above, the material of the blade substrate 11 needs to be selected in consideration of the triboelectrification series on the photoreceptor surface, and it is also necessary to select a material with good lubricity that is unlikely to cause damage or wear due to contact with the photoreceptor 1. be. Further, the tip portion of the blade substrate 11 and the photoreceptor 1
In order to prevent toner and dust from passing between the gaps 10 and 10, this tip is in close contact with the surface of the photoreceptor and automatically deforms in response to the waviness and eccentricity of the surface of the photoreceptor, thereby forming the gap 10 where corona discharge occurs. The blade substrate 11 should be made of a material with elasticity that allows the spacing to remain constant at all times. Examples of the material for the blade substrate 11 include polyurethane rubber, a plate made of thin metal or resin, and the like. At that time, if the material is conductive such as metal, the lead electrode 14 is coated with an insulator on the tip of the blade substrate 11.
It is necessary to prevent the photoreceptor 1 from becoming electrically conductive.

Since the resistor 15 causes a corona discharge in a minute gap between it and the surface of the photoreceptor, a predetermined current flows through the resistor 15.
Further, even if a small amount of dust should pass between the charging blade 9 and the photoreceptor 1, a resistor is used that will not burn out the photoreceptor layer 3 due to spark discharge. In addition, taking into account the copy speed, the space gap where corona discharge occurs, the capacitance of the photoreceptor 1, its charging potential, the applied voltage, its waveform, etc.
The resistance value of the resistor 15 should be determined, and its volume resistivity is usually set to about 104 to 1010 Ω·l. Furthermore, during discharge, it is inevitable that a small amount of ozone is generated, which is not perceivable, and therefore the resistor 1
As for No. 5, it is also important to select a material that is oxidation resistant, resistant to sputtering, and has excellent durability.

The voltage applied to the resistor 15 may be only a direct current, but as in this example, a voltage in which alternating current is superimposed on direct current is applied to the power source 13.
When the voltage is applied, corona discharge becomes stable and the surface of the photoreceptor can be charged more evenly.

Incidentally, the corona discharge generated between the resistor 15 and the photoreceptor 1 is easily affected by changes in the environment due to humidity and the like. For example, when humidity increases, it becomes difficult to discharge, and conversely, when humidity decreases, discharge becomes more likely to occur. Further, although the tip portion of the charging blade 9 that comes into contact with the photoreceptor 1 is made of a material that is resistant to wear, it is inevitable that some wear will occur if used for a long period of time. However, when such wear occurs, the distance of the discharge gap changes, which changes the current flowing through the lead electrode 14, which may cause the charged potential of the photoreceptor 1 to fluctuate.

From this point of view, in the charging device 4 shown in FIG.
1 is provided, and even if the environment changes or the discharge gap changes due to wear of the tip of the charging blade 9, the current flowing through the lead electrode 14 is controlled to be constant, and the current flowing through the lead electrode 14 is controlled to remain constant. The structure is such that the charging potential can be maintained constant. Such a constant current control device 21 is
Prior to charging the photoreceptor by the charging device 4, the surface of the photoreceptor 1 is neutralized by a static eliminator such as the static eliminator lamp 8 shown in FIG. It should be used when there is almost no triboelectrification. It is also possible to charge the surface of the photoreceptor after toner image transfer to a predetermined polarity by simply charging the surface of the photoreceptor with a charging device without providing a static eliminator. When the surface of the photoreceptor is to be frictionally charged to a relatively large negative polarity in some areas, the constant current control device 21 is abolished and the lead electrode 14 is controlled at a constant voltage. It is also possible to uniformly charge the surface of the photoreceptor.

In the experiment, polyurethane rubber, which has a high toner removal effect and excellent abrasion resistance, was used as the blade substrate 11. Lead electrodes 14 were coated in a layer on one side of the rubber, and a layer with a volume resistivity of 107 Ω was applied on top of the lead electrode 14. A charging blade 9 was used, which was coated with a resistor 15 made of about 100% resin in a layered manner. In order to prevent spark discharge during charging operation, the entire lead electrode 14 was covered with a resistor 15, and a gap d was provided between the leading edge of the lead electrode 14 and the resistor 15 in accordance with the resistance value of the resistor 15. (Figure 2). Such a charged blade 9 is
When installed in a copying machine (KR type OPC) manufactured by Ricoh Co., Ltd., a voltage of DC-900V with a superimposed ACIKHz sine wave was applied between the conductive base 2 of the photoreceptor 1 and the lead electrode 14 by the power supply 13. , the surface of the photoconductor is approximately -4
It was possible to uniformly charge the battery to 50 volts. The edge of the blade substrate 11 that comes into contact with the surface of the photoconductor has an edge of 40 to 6
Although it was worn by about 0μ, by providing the constant current control device 21, stable charging operation could be ensured.

By the way, as explained in the prior art section, a conventional charging roller consisting of a resistor layered around a conductor is
It performs charging operation by contacting the surface of the photoreceptor.
If there is a minute hole (pinhole) in the photosensitive layer of the photoreceptor, the conductive substrate underneath is exposed, and this portion comes into direct contact with the resistor of the charging roller. When this happens, spark discharge occurs between the resistor of the charging roller and the conductive base of the photoreceptor, and pinholes in the photoreceptor layer become increasingly enlarged, which may shorten the life of the photoreceptor. To prevent this problem, it is possible to increase the resistance of the resistor of the charging roller, but this will reduce the charging efficiency, so in order to charge the surface of the photoreceptor to a predetermined potential, it is necessary to increase the rotational speed of the photoreceptor. must be lowered, resulting in a decrease in copy speed.

However, in the charging device shown in FIGS. 1 and 2, the resistor 15 separates from the photoreceptor 1 and corona discharge occurs between the two, resulting in pinholes in the photoreceptor layer 3 of the photoreceptor 1. However, no spark discharge occurs. Therefore, it is possible to rotate the photoreceptor 1 at high speed.

As mentioned above, in the example shown in FIG. 2, spark discharge is prevented by separating the resistor 15 from the photoreceptor 1, but as shown in FIG.
If the distance Iad to the tip of the resistor 15 is made sufficiently larger than the thickness t of the resistor 15, the tip of the resistor 15 can be connected to the photoreceptor 1.
Even if the photosensitive layer 3 is brought into contact with the photosensitive layer 3, the spark discharge caused by the pinholes in the photosensitive layer 3 can be prevented. That is, by setting the distance d large as described above, the resistance value from the tip of the lead electrode 14 to the tip of the resistor 15 increases, so even if this tip is in contact with the photoreceptor 1, the pin This can prevent spark discharge caused by holes.

On the other hand, the corona discharge for charging the photoreceptor 1 is
Since this occurs at the small gap between the photoreceptor 1 and the resistor 15, indicated by the symbol X in the figure, it does not interfere with corona discharge.

In the example shown in FIG. 3, the resistor 15 is connected to the blade substrate 11.
After forming the resistor 15 up to the leading edge of the resistor 15 and assembling it as shown in FIG. By scraping it off, the tip of the resistor 15 is brought into smooth contact with the surface of the photoreceptor 1, as shown in FIG.

In the embodiment shown in FIG. 4, the charging blade 9 is pivotally attached to the machine frame of the copying machine via a pin 22 so as to be rotatable in the direction of the arrow. is pressed against. According to this configuration, even if the charging blade 9 is made of a rigid body, the blade 9 can be swung according to the undulations and irregularities on the surface of the photoreceptor, and the discharge gap can be kept constant.

In the embodiment shown in FIG. 5, the blade substrate 11 is made of a conductive material such as a metal plate, and a resistor 15 is directly formed thereon, so that the blade substrate 11 also serves as a lead electrode 14. In this case, as described above, an insulating material 11a such as resin or rubber having excellent sliding properties is attached to the tip of the blade substrate 11 and brought into contact with the surface of the photoreceptor.

In the embodiment shown in FIG. 6, a charging blade 9 is joined to the lower surface of a pressure member 31 that is slidably guided in a direction toward or away from the photoreceptor 1 by a guide member 30, By applying pressure toward the photoreceptor l by the compression spring 32.

The tip of the charging blade 9 is brought into contact with the photoreceptor l.

Further, in the embodiment shown in FIG. 7, the tip surface 11b of the blade substrate 11 faces the surface of the photoreceptor 1, and
1c is opposed to the rotational direction of the photoreceptor 1 and is in contact with the surface of the photoreceptor 1. A wedge-shaped gap 10 is formed between the tip surface 11b and the photoreceptor 1, and a resistor 15 covering the lead electrode 14 is integrally formed on the tip surface 11b. The charging blade 9 configured in this manner is biased by a spring in the direction indicated by the arrow P or Q, and the tip portion 11c is brought into pressure contact with the photoreceptor 1. According to this embodiment, the charging blade 9
The advantage is that the installation space can be reduced.

Other configurations of the embodiment shown in FIGS. 4 to 7 are as follows.

It goes without saying that the configuration can be the same as shown in FIGS. 1 to 3.

Although a specific example in which the object to be charged is a photoreceptor has been described above, the present invention can be widely applied to other objects to be charged, such as when charging a dielectric belt that conveys a sheet such as copy paper. It is something.

(Effects of the Invention) As described above, the charging device according to the present invention can suppress the amount of ozone generated, prevent uneven charging on the surface to be charged, simplify the structure, and reduce its cost.

[Brief explanation of drawings]

FIG. 1 is a general configuration diagram showing an example of an electronic copying machine using a charging device according to the present invention, FIG. 2 is an enlarged sectional view of the charging device shown in FIG. 1, and FIGS. 3 to 7 are FIG. 7 is a diagram showing other embodiments of the charging device. 9...Charged blade 10...Gap 15...Resistor

Claims (1)

[Claims] The charging blade has a charging blade disposed such that the tip portion thereof is in contact with the charged body opposite to the moving direction of the charged body and forms a wedge-shaped gap between the charging blade and the charged body, the blade having:
A charging device comprising a resistor serving as a discharge electrode to which a voltage is applied, in a portion facing a charged object.